1. Field of the Invention
The invention relates to a radial piston pump for high-pressure fuel supply in fuel injection systems of internal combustion engines, in particular in a common rail injection system, having a plurality of pump elements, disposed radially to a drive shaft, each of the pump elements having a pumping chamber that is defined on one end by a piston, having one intake-side inlet conduit per pump element, wherein the inlet conduits are supplied with fuel via an annular conduit, defined by the drive shaft and a housing, and discharge into the pumping chambers of the pump elements.
2. Description of the Prior Art
In radial piston pumps of the type with which this invention is concerned, the pumping quantity is as a rule controlled by means of intake throttling. If two pump elements are simultaneously aspirating fuel from the annular conduit, then at low feed quantities, especially feed quantities of less than 30% of the full feed quantity, it can happen that one of the pump elements will fail completely and not pump any longer. This leads to an unequal demand for torque by the high-pressure fuel pump and hence to rough operation of the engine. This rough operation of the engine is especially problematic in idling.
It is known to overcome this for instance by means of a controlled intake valve, in which the spring of the intake valve is disposed in the piston of the pump element. A disadvantage of this embodiment is the increased idle space and the poorer efficiency and the size of the high-pressure fuel pump.
Another way of solving this problem could be to provide one metering unit per pump element, instead of one metering unit for the entire high-pressure fuel pump. This solution fails, however, among other reasons because of high costs and the space needed for additional metering units.
The primary object of the invention is to furnish a high-pressure fuel pump in which the pump elements pump uniformly even in the partial-load range and which compared with known high-pressure fuel pumps requires no additional structural volume and moreover can be produced extremely economically.
In a radial piston pump for high-pressure fuel supply in fuel injection systems of internal combustion engines, in particular in a common rail injection system, having a plurality of pump elements, disposed radially to a drive shaft, each of the pump elements having a pumping chamber that is defined on one end by a piston, having one intake-side inlet conduit per pump element, wherein the inlet conduits are supplied with fuel via an annular conduit, defined by the drive shaft and a housing, and discharge into the pumping chambers of the pump elements, this object is attained in that the hydraulic communication between the annular conduit and the inlet conduits is controlled by the drive shaft.
Because of the control according to the invention of the hydraulic communication between the annular conduit and inlet conduits, it is assured that at all times, that is, in every position of the drive shaft, only one pump element can aspirate fuel from the annular conduit. Thus in the partial-load range, this prevents the possibility of a plurality of pump elements aspirating simultaneously, so that one of these pump elements can no longer aspirate any fuel at all and hence can no longer pump any fuel. In the high-pressure fuel pump of the invention, each pump element, during its intake stroke, can aspirate the entire fuel quantity flowing through the metering unit into the annular conduit. Therefore even in the partial-load range, where feed quantities are very slight, the pump elements still function well. The torque required by the high-pressure fuel pump is therefore virtually constant over one revolution of the drive shaft, and thus the internal combustion engine still operates smoothly even during idling.
In a further feature of the invention, it is provided that the drive shaft is embodied as a rotary slide, so that the control of the hydraulic communication between the annular conduit and the inlet conduits can be done in the simplest possible way, virtually without needing additional space. Depending on how the rotary slide is designed, the control times can be adapted in a simple way to the requirements of the fuel injection system.
In another feature of the invention, it is provided that during the intake stroke of a pump element, this element communicates hydraulically with the annular conduit, and/or that regardless of the position of the drive shaft, only one inlet conduit is ever in hydraulic communication with the annular conduit at a time, so that only one pump element at a time can aspirate the entire fuel quantity flowing into the annular conduit, and as a result optimal intake conditions for the pump elements prevail.
Alternatively, it can also be provided that regardless of the position of the drive shaft, at least one inlet conduit does not communicate hydraulically with the annular conduit. This means that a plurality of inlet conduits, but not all the inlet conduits, communicate simultaneously with the annular conduit, which makes the pumping flow of the prefeed pump more uniform without having to do without the advantages of the invention in terms of the operating performance of the high-pressure fuel pump.
Another feature of the invention provides that the fuel inflow in the annular conduit is controlled by a metering unit, so that the feed quantity regulation of the high-pressure fuel pump of the invention can be accomplished in a time-tested way that is known per se.
To prevent a reverse flow of fuel out of the pump element into the annular conduit, a check valve is disposed in each inlet conduit.
To increase the operating reliability and to simplify production, it is also provided that the inlet conduits are disposed in the housing; in an especially preferred embodiment, the inlet conduits extend essentially radially to the longitudinal axis of the drive shaft.
In a further feature of the invention, it is provided that the annular conduit is sealed off from the lubrication of the high-pressure fuel pump, so that the pump element cannot aspirate any fuel that is meant to serve solely to lubricate the high-pressure fuel pump, thus making precise feed quantity regulation possible.